The preparation of 11(12)-pentadecen-15-olides advantageously proceeds starting from 13-oxabicyclo[10.4.0]hexadec-1(12)-ene (DDP). 1-Hydroperoxy-16-oxabicyclo[10.4.0]hexadecane (DDP hydroperoxide, DDP-OOH) is obtained by acid-catalyzed addition of hydrogen peroxide on to DDP. Cleavage of the DDP-OOH to form the macrocyclic ring is to be regarded as the second step in the synthesis to give the 11(12)-pentadecen-15-olides. This cleavage is usually carried out in the presence of catalysts such as Cu(OAc)2 and, where appropriate, FeSO4. If this reaction stage is carried out purely by means of heat, the reaction product contains considerable amounts of the saturated compound 15-pentadecanolide, which is indeed a musk aroma, but has different smell characteristics to the 11(12)-pentadecen-15-olides and should therefore be formed in only the smallest possible amounts. Furthermore, the high formation of residues (e.g. distillation bottom product) is a disadvantage of the cleavage purely by means of heat.
DDP is conventionally obtained by acid-catalyzed cyclization, with splitting off of water, of 2-(3-hydroxypropyl)-1-cyclododecanone (OCP), which in turn can be synthesized by free-radical addition of allyl alcohol on to cyclododecanone (e.g. in DE-OS 2 136 496).
The process for the preparation of the 11(12)-pentadecen-15-olides can be illustrated by the following equation:

In EP-A 424 787, OCP was homogenized in 4.6 weight equivalents of glacial acetic acid at room temperature, a cold 25% strength by weight aqueous solution of sulfuric acid (about 51 mol % (about 21 wt. %), based on the OCP) was added and the reaction mixture was then cooled to 0° C. Thereafter, 1.65 molar equivalents of H2O2 (70% strength by wt. solution) were added, the temperature rising to 7° C. After a short after-reaction time, the solid formed (DDP-OOH) was filtered off and this was washed with water and aqueous NaHCO3 solution and dried; the yield was 80%.
Cleavage of the DDP-OOH was carried out by introducing the DDP-OOH in portions into a saturated solution of Cu(OAc)2 in methanol (prepared from about 94 mol % Cu(OAc)2 and 12.3 parts by weight of methanol, based on the DDP-OOH; the concentration of DDP-OOH in this amount of methanol was about 0.25 mol/l). The addition of 2 portions of FeSO4 (in each case just about 20 mol %, based on the DDP-OOH) and stirring overnight at room temperature followed. For working up, the mixture was added to saturated aqueous NaCl solution and extracted with diisopropyl ether and this extract was washed with saturated aqueous NaHCO3 solution and saturated aqueous NaCl solution. After drying and fractional distillation, 73% of theory of 11(12)-pentadecen-15-olides, which also contained 8% of 15-pentadecanolide, was obtained.
In Russ. Chem. Bull. 1998, 47, 1166–1169, DDP was initially introduced into 5.2 weight equivalents of glacial acetic acid at 0° C., and a mixture comprising a 50% strength by wt. aqueous solution of sulfuric acid (about 26 mol % (=11 wt. %), based on the DDP) and 30% strength by wt. hydrogen peroxide (about 1.89 molar equivalents) was added. After a short after-reaction time, the solid formed (DDP-OOH) was filtered off and this was washed with a 50% strength acetic acid solution (80 wt. %, based on the DDP) and then several times with water (4 washing operations with in each case 2 parts by weight of water, based on the DDP) until the wash water was neutral. After drying of the solid, 85% of theory of DDP-OOH, which had a purity of 96%, was obtained.
Cleavage of the DDP-OOH was carried out by metering a suspension of 1 portion of DDP-OOH and about 3.8 portions by weight of 4-methylpentan-2-one (MIBK) into a boiling solution of Cu(OAc)2 in about 3.8 portions by weight of MIBK (based on the DDP-OOH) over a relatively long period of time. The amount of Cu(OAc)2 was varied in the range from 0.15 to 7.0 mol %, based on the DDP-OOH, according to the authors the optimum being 5 mol % Cu(OAc)2. After 3 hours of after-reaction time at the boiling point, the reaction mixture was cooled and freed from the copper salts which had precipitated out. The filtrate was washed with hot water (2 washing operations with in each case 7.7 weight equivalents of water, based on the DDP-OOH) and concentrated. Using 5 mol % Cu(OAc)2 a crude yield of 11(12)-pentadecen-15-olides of 96.5% of theory was obtained.
Disadvantages of these processes are, in particular, the precipitating out of elemental copper and/or insoluble copper compounds under the reaction conditions of the cleavage of DDP-OOH and the large amounts of reagents and auxiliary substances used in the reactions. Further disadvantages which are to be mentioned are, for example, the many, in some cases expensive process steps and the unsatisfactory space/time yield. Washing of the DDP-OOH crystals, in some cases until the wash water is neutral, not only is expensive and environmentally unfriendly, but also makes clear that residues of acid in the DDP-OOH are to be avoided for the subsequent stage of fragmenting. The isolation of the DDP hydroperoxide, which not only is expensive, but also presents safety problems, since hydroperoxides have a high risk potential, is a disadvantage in particular.
The known synthesis processes are therefore unsuitable for an industrial reaction. An industrial process which provides 11(12)-pentadecen-15-olides in a simple and inexpensive manner is therefore of great economic interest.
With the present invention, it is possible to overcome the disadvantages mentioned and to provide an industrially favourable process. The process according to the invention is particularly suitable for use on an industrial scale.